1. Field of the Invention
The present invention relates to a protection circuit. More specifically, the present invention relates to a protection circuit capable of preventing damage from the over-voltage.
2. Descriptions of the Related Art
Referring to FIG. 1, a conventional over-voltage protection circuit structure 1 for protecting a high power translation circuit is illustrated. The over-voltage protection circuit structure 1 comprises a voltage detection module 110 and a relay circuit 134. The relay circuit 134 comprises a switch 116 and an inrush resistor 117 connected in parallel with the switch 116. The high power translation circuit comprises a power correction module 111, a direct current to direct current (DC/DC) module 112 and an auxiliary power supply 113. The power correction module 111, the DC/DC module 112 and the auxiliary power supply 113 are all well-known to those skilled in the art, and therefore no further description thereof will be made herein. The voltage detection module 110 is configured to detect a voltage across alternating current (AC) terminals 114 and 115. When the voltage go excessively high, the voltage detection module 110 merely opens the switch 116, with the AC voltage still passing through the inrush resistor 117 and a bridge rectifier 118 into the circuit continuously. When the AC voltage reaches a certain value, breakdown usually occurs in such elements as lightning arresters, power transistors and capacitors, thus causing damage to the circuit.
FIG. 2 illustrates a conventional way to make improvement on this shortcoming, which is a conventional over-voltage protection circuit structure 2. The over-voltage protection circuit structure 2 differs from the over-voltage protection circuit structure 1 in that, in the relay circuit 234, an auxiliary switch 220 is connected in series with the inrush resistor 117, both of which are then connected in parallel with the original switch 116. Once an AC over-voltage occurs, the voltage detection module 110 quickly opens the auxiliary switch 220 and the switch 116 in sequence, thus preventing the AC voltage from being delivered into the circuit. Additionally, a bulk capacitor 119 is configured to supply energy to the auxiliary power supply 113, which in turn supplies power to the power detection module 110. The power detection module 110 also detects a voltage across the bulk capacitor 110, and once this voltage drops smaller than a certain preset recovering value, the power detection module 110 closes the auxiliary switch 220 and the switch 116 in sequence, so that the AC voltage of the circuit recovers through the auxiliary switch 220 and the switch 116. If the AC voltage stays excessively high continuously, the voltage detection module 110 quickly opens the auxiliary switch 220 and the switch 116 in sequence again to prevent from that the AC over-voltage is delivered into the circuit. Once again, the bulk capacitor 119 supplies energy to the auxiliary power supply 113, i.e., the bulk capacitor 119 begins to discharge. Therefore, when the AC voltage stays high continuously, the auxiliary switch 220 and the switch 116 are opened at first, and then closed after the bulk capacitor 119 is discharged for a time of period, and again opened immediately upon detection of an over-voltage. This operating cycle is repeated over and over again according to the aforesaid voltage status.
Unfortunately, after long periods of opening and closing operations, carbon deposition tends to occur on contacts of the auxiliary switch 220 and the switch 116, causing failure to open after the switches are closed. As a consequence, the entire circuit will fail to work and the AC over-voltage is delivered continuously into the circuit to cause disruption. Furthermore, such a circuit cannot actively detect an AC voltage on a continuous basis; rather, the voltage detection module 110 cannot continue to determine occurrence of an AC over-voltage until the auxiliary switch 220 and the switch 116 are closed to allow delivery of the AC voltage into the circuit.
In summary, efforts still have to be made in the art to ensure that the voltage detection module 110 can still detect and determine an over-voltage continuously while the auxiliary switch 220 and the switch 116 are opened, so as to reduce frequency to open and close the auxiliary switch 220 and the switch 116. This helps to prevent failure of the auxiliary switch 220 and the switch 116, and maintain a voltage of the bulk capacitor within a reasonable and safe range, thus accomplishing the goal of protecting the overall circuit.